This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our studies aim to dissect the earliest events in rectal HIV/SIV infection in order to understand how HIV infection is established and spreads, and explore novel immunomodulatory strategies to prevent mucosal infection. Toll-like receptor (TLR) agonists can boost innate immunity through DC activation, with TLR3 the best characterized receptor of viral dsRNA. Poly(IC) is a synthetic dsRNA analog known to activate human and macaque DCs through both TLR3-dependent and independent mechanisms, and clinical grade poly(IC) (poly(ICLC) or Hiltonol) is commercially available and being used in humans, underscoring the potential for this mode of activation to be developed as an anti-HIV strategy. We have shown in vitro that poly(IC) signaling blocks HIV infection in DCs and DC-T cell co-cultures. Thus, we hypothesized that rectal application of Hiltonol in vivo might similarly activate mucosal DCs, triggering their immunostimulatory capability and limiting SIV replication while boosting protective immune responses. We are comparing the effects of Hiltonol on rectal challenge of Indian rhesus macaques with wt and the attenuated virus [unreadable]nef (nef deletion mutant) because we postulated that the effects of Hiltonol would be more pronounced in a setting devoid of the immune suppressive effects of nef, and where the attenuated replication of [unreadable]nef and its protective capacity against subsequent wt challenge would be enhanced. Following Hiltonol application and challenge, we are continuing to follow the animals over time for viral and immune parameters elicited in response to Hiltonol/SIV: plasma viral load, changes to blood DC and T cell subset numbers and activation, CK/CC levels, Ab production, and T cell responses (ELISPOT for IFN gamma and ICS for IFN gamma, TNF gamma, IL-2, and IL-17 secretion).